You might think that Jupiter is actually a friendly planet because it protects the Earth by shielding us from potentially hazardous impactors such as comets. It is true that Jupiter slings some long-period comets out of the solar system and destroys some others, eliminating these objects from the list of things that could slam into Earth with devastating results. However, whether Jupiter actually decreases the number of comets that impact our planet has been called into question, and a study published in Astrobiology last year suggests that the idea is completely false.

What's more, asteroids pose a greater threat to Earth than comets, being far more common. And rather than shielding our planet, Jupiter has a tendency to hurl them toward us. The asteroid belt is full of rocks that never had a chance to coalesce into planets, mainly due to Jupiter's gravitational interference while it was stomping around the early solar system, crushing infant planetoids. It is not uncommon for the gas giant to nudge these rocks into the inner solar system where they have a greater chance of intersecting with Earth's orbit.

Does this really sound like the type of entity that would shield us from harm? No, it sounds like a great metallic orchestra of death beckoning us to our doom.

Just look at the objects that are foolish enough to get close to Jupiter. Io, Jupiter's innermost large moon, has been reduced to a volcanic hellscape. The gravitational forces from Jupiter grind the moon's rock together. Io's surface is covered in endless pools and rivers of burning lava punctuated by towering volcanic eruptions. Jupiter's moon Europa, meanwhile—often considered a watery sanctuary where life could exist—has had its icy surface scorched an orangish brown by the endless stream of high-energy particles shooting out from its cruel master of a planet.

A sequence of five images of Io taken by NASA's New Horizons probe on March 1 2007 over the course of eight minutes. The images form an animation of an eruption in the Tyashtar Paterae volcanic region. The plume is 330 km high, though only its uppermost half is visible in this image as its source lies over the moon's limb on its far side.

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As for the two spacecraft we have sent to orbit Jupiter—Galileo and the currently orbiting Juno—NASA engineers had to take great precautions to shield the spacecraft's instruments from the endless bombardment of radiation from Jupiter's immense magnetosphere. Juno has a 400-pound titanium vault to shield its internal components from Jupiter's radiation, and even then, the spacecraft is flying so close to the hostile planet that the total operating time is estimated to be only a year and a half. Much longer in the ruthlessly unforgiving environment around Jupiter and the electronics of the spacecraft will be inevitably fried. Remember, that's just from flying near the planet—not within the clouds themselves.

Galileo, which orbited Jupiter from December 1995 to September 2003, was able to fair a little better because it kept a safer distance. Still, almost two years before the mission was terminated, Galileo's cameras needed to be deactivated because they had been irreparably damaged by radiation. The Galileo team worried that they would lose contact with the spacecraft entirely during the final phases of the mission, and they crashed Galileo into the Jovian beast before that could happen—surly a welcome end for the craft that had suffered so long under the scourge of Jupiter's burning radiation.

Jupiter's Toasty Cousins

Originally, astronomers assumed that our solar system represented a typical arrangement of planets around a star, with the little rocky planets in close and the big gas giants farther out. As we are continuing to learn, solar systems throughout the galaxy are not the same. If anything, our little neighborhood is an oddity rather than the norm.

The turbulent atmosphere of a hot, gaseous planet known as HD 80606b is shown in this simulation based on data from NASA's Spitzer Space Telescope.

One of the most common kinds of planets we find orbiting other stars are so-called "hot Jupiters," demon cousins to our own cruel giant. These burning planets, about the size of Jupiter, orbit very close to their host stars, sometimes even closer than Mercury orbits the sun. The result is that they are astonishingly hot, highly volatile, and often circle their parent stars in a matter of days or weeks. The hottest known planet, WASP-33b, has blistering surface temperatures around 3,200 degrees C (5,790 F), which is hotter than the surface of some red dwarf stars.

These roaster planets, as they are sometimes called, are tidally locked with their stars, so one face of the planet is always receiving a bombardment of heat and stellar radiation. This makes for some truly chaotic weather. Chunks of a hot Jupiter's atmosphere can get blasted away by solar flares and eruptions coming from the host star.

If Jupiter were ever forced in close to the sun again—say, from the gravitational influence of a rogue planet passing through the solar system in the distant future—it could be captured in a new orbit close to the sun and ignite into a fiery version of its already savage self.

Of course, if Jupiter did move in close, it would completely disrupt the inner solar system, ejecting all four rocky planets out into the void before it had a chance to burn us. Let's just hope this bully stays out beyond the asteroid belt where it belongs.